Snap action device



Nov. 26, 1957 -T.VN. FLIGHT ET AL 2,314,635

SNAP ACTION DEVICE Filed Oct. 26; ,1955 2 Sheets-Sheet 1 INVENTORS AT TORNEYS Nov. 26, 1957 T. N. FLIGHT ETAL 2,814,685

SNAP ACTION DEVICE Filed Oct. 26, 1955 -2' SheetsSheet 2 :1 "I" ""I I MI [I V 2a 24 I z I g l l 14 18 E i 25 m 22 FIG.8, 26

-INVENTOR5 ATTORNEYS United States Patent SNAP ACTION DEVICE Theodore N. Flight, Farnham Common, and Arthur Chinn, Slough, England, assignors to The Rheostatlc Company Limited, Slough, England, a British company Application October 26, 1955, Serial No. 542,985

Claims priority, application Great Britain October 28, 1954 8 Claims. (Cl. 200-67) This invention is concerned with snap action devices comprising an internally stressed metal sheet in which a snap movement of one part of the sheet is derived from the sudden release of stress imposed by the gradual movement of an actuator applied to another part of the sheet.

Such snap action devices have been made from a sheet of metal by cutting slots adjacent to two parallel edges and corrugating or twisting the edge limbs so formed to place these limbs in tension and the centre limb in compression. They have also been made by forming a sheet with two parallel slots originating at one edge of the strip and terminating before reaching the opposite edge so as to form three parallel limbs. The two outer limbs are then placed in tension and the middle limb in compression with its free end pressing against a pivot support. Alternatively the outer limbs of such a sheet have been fixed to a base in such manner as to deform the slots from parallel to tapering thus putting the sheet in an unstable condition.

In accordance with the present invention an internally stressed metal sheet or strip is made from a metal sheet without slotting or cutting but by forming intermediate the length of the sheet several corrugations running from side to side of the sheet and flattening the corrugations slightly where they meet the edge of the sheet, thus putting the two parallel corrugated edges in compression compared with the centre corrugated portion. This extra length of metal at the edges resulting from the slight flattening of the corrugations is accommodated by a twisting action on the sheet, the two sides concerned twisting in opposite directions causing the edges of the sheet parallel to the corrugations to lie at an angle to one another. If now one edge parallel to the corrugations be supported from a base and force be applied to the sheet at one of the unsupported corners substantially at right angles to the plane of the sheet such twisting action will result in snap movement of the unsupported end of the sheet from one position of rest to another. Such positions of rest are not necessarily positions in which the sheet is in a condition of internal equilibrium as stops may be provided to arrest the movement of the sheet before it has arrived at such equilibrium position. The sheet will under such conditions press upon the stops and will at the same time be more sensitive to changes of pressure or movement of the actuator. The supporting of one edge of the sheet as described gives a non-self-returning action and operation in both directions can be obtained only by reversal of the initiating force or movement as applied to the sheet.

It is possible to make such a snap-action device selfreturning to its initial position after the removal of the initiating force. If the sheet be rigidly supported at one corner on a post or like support and pressure he applied to the sheet by a second support (which may be adjustable) at some point intermediate the supported corner ice and the centre of the uncorrugated side then snap action will be obtained from the movement of the opposite uncorrugated side when a slowly moving actuator is applied to the second corner of the supported uncorrugated side. This snap action will be self-returning when the force of the actuator is withdrawn.

It is possible to use such a formed sheet in several ways to operate switch contacts, to open and close a valve or to operate a damper or the like in each case giving a positive snap movement from the gradual movement of an actuator.

Various embodiments of the invention are illustrated diagrammatically in the accompanying drawings in which Fig. 1 is a plan view of a rectangular sheet formed in the manner described while Fig. 2 is a side elevation of such a formed sheet, the twist being accentuated in the drawing to make the action clear. Figs. 3 and 4 are side elevation and plan views respectively, of a simple snap action switch in which the formed sheet is supported at one end the opposite end, of the sheet carrying one contact on an extension of one corner while the initiating force or movement is applied to the sheet at .a point at the same end. Figs. 5, 6 and 7 are end view, side view and plan view respectively, of a construction in which the snap action is self-returning on the removal of the initiating force. Fig. 8 is an elevational view partly in section which illustrates the application of the device to a gas control thermostat.

In the various figures of the drawings A indicates the formed sheet of metal. Referring to Fig. 1, four corrugations are indicated at 1, 2, 3, 4, the variation of shading indicating the reduction of the depth of corrugation at the edges of the strip which produces the stress within the strip to cause it to take the form shown in Fig. 2.

In the simple switch employing the device of the invention shown in Figs. 3 and 4 the sheet A is supported across its width at one end while a contact 5 carried by the sheet presses against a contact 6 which is so positioned as to arrest the movement of contact 5 before the sheet has moved to its position of final equilibrium thus producing pressure between the contacts 5 and 6.

An actuator indicated by the arrows 7 engages the sheet at a point at the same end of the sheet as the contact. As this actuator 7 is moved slowly up and down, the corner carrying contact 5 of the sheet passes with a snap action from pressing on contact 6 to pressing against a backstop 8 which is in turn positioned to arrest the sheet before it has passed to its second equilibrium position.

In the construction shown in Figs. 5, 6, 7 both corners of one end of the sheet A are extended as indicated clearly in Fig. 7 to carry contacts 9 and 10 co-acting alternately with contacts 11 and 12 mounted on a base B. The centre point of the width of the sheet between the contacts 11 and 12 is supported at 13 from the base B and is held in contact at this centre point by a spring tongue 14 extending from a plate C supported from the base B, the tongue pressing on the top of the sheet A.

One corner of the sheet at the opposite end from the contacts and indicated at D in Fig. 7 is supported from the base B and a stop screw 15 presses the sheet A upwards from the base. The actuating pressure is applied at any point 16 between this screw 15 and the opposite corner from D at the same end of the sheet.

In the construction of gas control thermostat illustrated in Fig. 8 the formed sheet A is shown as supported at one corner 17 of the sheet by a post 18 rising from the instrument base 19. Pressure is applied to the sheet near support point 17 by a tongue as indicated at 20. Extending from the base 19 is a tube 21 of relatively high expansion metal joined at its end remote from the base to a relatively non-expanding rod 22 which is brought through the base to press the sheet A at a point 23 intermediate the pressure point at and the edge of the sheet and in opposition to pressure at point 20. A valve disc 24 is attached to the sheet A at the diagonal corner from that at which the rod 22 presses on the sheet. The valve seat is shown at 25 and the gas inlet and outlet ports are indicated at 26--27. In operation pressure at point 20 is so set that as the pressure of rod 22 is reduced due to the heating of the expanding tube 21 the corrugated sheet A takes up the position shown in the drawing in which the corner of the sheet carrying the valve 24 has moved towards the base and closed the inlet port 26. A gradual fall in temperature of the tube 21 moves the rod 22 to press on the sheet until the opposite end carrying the valve 24 moves with snap action to open the valve.

While in the construction shown in Fig. 8 the initiating movement applied to the sheet is generated by diflerential expansion of metals with temperature change, obviously the initiating movement may be generated by the expansion of a capsule or bellows with pressure change associated with the capsule or bellows, or may be applied by a manual operation.

Moreover, while this invention concerns the formation of a snap action device from a metal sheet without cuts or slots but by the differential stressing of the sheet in the manner described it does not exclude the shaping of the sheet to provide contact carrying parts or parts for alternative fixing positions. It is not intended to limit the operating force to the pressure or movement of an actuator applied to one point on the sheet. A snap action of one part of the sheet may be obtained from a twisting action applied to the opposite end of the sheet.

We claim:

1. A sheet of metal formed initially with at least one corrugation running transversely of the sheet from one edge to the opposite edge of the sheet, said corrugation being thereafter deformed by at least partial flattening of the corrugation near the said two edges of the sheet so as to place each such corrugated edge in compression relative to the body of the sheet between the deformed edge portions.

2. A strip of metal formed with a plurality of corrugations running transversely of the strip from one edge to the opposite edge of the strip, said corrugations being deformed by partial flattening of the corrugations near the two edges of the strip so as to place each such corrugated edge in compression relative to the body of the strip between the deformed edge portions.

3. A snap action device comprising a sheet of metal formed with corrugations running transversely of the sheet from one edge to the opposite edge of the sheet, said corrugations being deformed by partial flattening of the corrugations near the two edges of the sheet so as to place each such corrugated edge in compression relative to the body of the sheet, a base supporting said sheet at one corner thereof, and means for applying an initiating movement to the sheet between the support point and the corner of the sheet on the same uncorrugated side.

4. A self-returning snap action device comprising a sheet of metal formed with corrugations running transversely of the sheet from one edge to the opposite edge of the sheet, said corrugations being deformed by partial flattening of the corrugations near the two edges of the sheet so as to place each such corrugated edge in compression relative to the body of the sheet, means for applying an initiating movement to the sheet between the support point and the corner of the sheet on the same uncorrugated side, and means for applying pressure to the sheet on the same uncorrugated side intermediate the fixing and the point of application of said initiating movement and in opposition to said initiating movement.

5. In a snap action device a prestressed snap acting metal sheet initially corrugated from one edge to an opposite edge, the corrugated portions of the sheet along said edges being thereafter deformed to have less corrugation depth relative to the corrugation depth of the intervening corrugated portion of the sheet, whereby said corrugated portions of less depth along said edges of the sheet are in compression relative to said intervening corrugated portion of the metal sheet.

6. A snap action device comprising a sheet or strip of metal which is neither slotted or cut but is formed with one or more corrugations passing from one edge of the sheet to the other, which corrugations are partially flattened near each edge of the sheet to produce internal stresses within the sheet which twists in such manner that the two uncorrugated sides of the sheet lie at an angle to one another in the plane of the sheet.

7. A snap action device as claimed in claim 6, including means for supporting the sheet along one uncorrugated side, and an initiator applied to a point on the other uncorrugated side of the sheet the gradual movement of which produces a snap movement of the unsupported side of the sheet causing it to assume a reversed position relative to the plane of the sheet.

8. A snap action device as claimed in claim 6, including means for supporting the sheet at one corner, and an initiator applied to the uncorrugated supported side of the sheet the movement of which produces a snap movement of the unsupported uncorrugated side of the sheet causing the unsupported side to assume a reversed position relative to the plane of the sheet.

References Cited in the file of this patent UNITED STATES PATENTS 725,220 Contant Apr. 14, 1903 1,331,677 Schachter Feb. 24, 1920 1,678,407 Spencer July 24, 1928 1,895,592 Spencer Jan. 31, 1933 2,084,982 Anderson et al June 29, 1937 2,102,656 Vaughn Dec. 21, 1937 2,204,792 Davis June 18, 1940 2,230,720 Jarvis Feb. 4, 1941 2,332,883 Abrahamson Oct. 26, 1943 2,469,217 Sway May 3, 1949 2,469,686 Eaton May 10, 1949 2,511,526 Bugge June 13, 1950 2,613,874 Thomas Oct. 14, 1952 2,700,079 Haydon Jan. 18, 1955 2,706,226 Welsh Apr. 12, 1955 

